<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>画三角形</title>
    <style>
        #trign{
            width: 0px;
            height: 0px;
            border-top: 100px solid red;
            border-right: 100px solid white;
            border-bottom: 100px solid black;
            border-left: 100px solid yellow;
        }

    </style>
</head>
<body>
    <div id="trign"></div>
</body>
</html>